The 25-year-old former Italy Under-21 international has penned a contract with Inter until June 2018.
A statement from Inter read: "Danilo D'Ambrosio is an Inter player. "The documents by which the Nerazzurri club has acquired the Torino defender on a permanent basis have been presented to the Lega Serie A."
D'Ambrosio has scored two goals in 14 league appearances for Toro this season and is Inter's first reinforcement of the winter transfer window.
Inter are fifth in the Serie A standings and travel to Turin on Sunday to face leaders Juventus.